The goal of this proposal is to test the hypothesis that trace elements from World Trade Center (WTC) dust, gas or fumes remain present in human tissues years after 9/11/2001 and, thus, may be useful in developing biomarkers of cumulative WTC exposure. Our project will work towards the research objective of the Zadroga Act of expanding knowledge of the health effects of the World Trade Center disaster. Using in vivo x-ray fluorescence (XRF), we found that Ti and Sb may have been absorbed and retained in the bones of some WTC survivors. We now wish to pursue this hypothesis further by analyzing trace elements in tissues of deceased individuals enrolled in the World Trade Center Health Registry (WTCHR) who were autopsied by the Office of the Chief Medical Examiner (OCME) of the City of New York. Tissues from approximately 100 index autopsies of WTCHR registrants conducted in 2007-2011 will be available for study, along with tissues from 50 matched control autopsies. Control autopsies will provide measures of background concentrations of trace elements resulting from normal urban life. Interview data from the time of enrollment will be available for index autopsies and will reveal correlations between tissue concentrations of WTC trace elements and WTC exposure estimated from interview responses. We also will compare concentrations of trace elements in different organs of subjects in the WTCHR with those obtained from animals exposed to WTC dust via intratracheal inhalation. Support of the study hypothesis will inspire additional research to develop biomarkers indicative of cumulative exposures to WTC contaminants. Etiologic studies of diseases observed among WTC survivors and medical treatments might be improved with better understanding of the body burden of WTC contaminants.